A solar cell generally consists of a p-n junction or p-i-n junction with silicon (Si) or compound semiconductors formed on a substrate to convert sunlight incident onto its front surface into electricity. In order to increase the electric power generation, a solar cell utilizing sunlight incident on the back surface as well as front surface is proposed. Such a solar cell has, for example, a configuration shown in FIG. 7, and is fabricated by depositing a p-type amorphous Si (p-type a-Si) film 102 and an n-type amorphous Si (n-type a-Si) film 103 on the respective surfaces of i-type crystal silicon 101 using a plasma CVD method, and then by forming a transparent electrode 104 using a sputtering method and current collective electrodes 105 using a screen printing method on both surfaces.
For example, a parallel-plate type plasma CVD apparatus shown in FIG. 8(b) has been mainly used for the deposition of the a-Si film. This apparatus is composed of a load lock chamber 110, a heating chamber 120, a plasma CVD (PCVD) chamber 130 to deposit the a-Si film, and a cooling chamber 140. The adjacent chambers are connected through a gate valve 106. The i-type silicon substrates 101 are mounted on a substrate holder 107, which acts as a backing plate, as shown in FIG. 8(a) and is transported in the direction of the arrow of FIG. 8(b). That is, after substrates are mounted on the substrate holder as shown in FIG. 8(a), the substrate holder is transported to the load lock chamber 110, and the chamber is thereafter evacuated. Then, the gate valve is opened to transport the substrate holder to heating chamber 120. After the substrates are heated to a predetermined temperature using a heater 121, the substrate holder is transported to parallel-plate type PCVD chamber 130. When the substrate holder is transported into PCVD chamber 130, a film forming gas (SiH4/PH3 gas) is introduced into the PCVD chamber 130 and high-frequency power is fed to a powered electrode 131 to generate plasma and form the n-type a-Si film on silicon substrate 101. Then, the substrate holder is transported to cooling chamber 140.
After the substrate temperature drops, the venting gas is introduced into the cooling chamber 140 to the atmospheric pressure. The substrate holder 107 is taken out and the substrates are turned over in order to form the p-type a-Si film on the other surface of substrate. The substrate holder is sent into the load lock chamber of the plasma CVD apparatus shown in FIG. 8(b) and the p-type a-Si film is deposited in the same manner as mentioned above. Thus, the p-i-n junction is formed. Here, SiH4/B2H6 gas is introduced into the PCVD chamber as film forming gas.
Then, a transparent conductive film such as ITO is formed on both surfaces of the silicon substrate 101 in the sputtering apparatus. Finally, current collecting electrodes are formed using, for example, the screen printing method to complete the solar cell.